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We identify the role of transverse modes in causing temporal instability in an all-solid-state laser system and thus propose a new method to trigger deterministic optical rogue waves. Experimental investigations show that the near-degenerate transverse modes with mode frequency difference close to the relaxation oscillation frequency is responsible for the rogue waves. By tilting the reflective mirror, the transverse modes beating frequency decreases and gets close to relaxation oscillation frequency, thus the system exhibits self-pulsing behavior and rarely-arising giant pulses. The statistical distribution of the pulse intensity deviates from the exponential statistics to the L-shaped distributions with long tails, indicating the appearance of optical rogue waves. The conclusion can be extended to other Class-B lasers where the population inversion cannot be eliminated adiabatically.

We first demonstrate the laser performance of a compact 2.06- $\mu$ m Ho: YLF laser wing pumped by a fiber-coupled laser diode, which is insensitive to the polarization state of pump source. A maximum output power of 1.44 W, corresponding to a slope efficiency of 41.25%, is obtained. The optimized beam quality factor reaches 2.52 when the output power is about 1 W. Multi-peak laser spectra are observed in the range of 2064.5–2066.6 nm. The output power fluctuation is greatly reduced to about 0.57% of the average power in 50 min. The degree of polarization reaches the level of 96%. The performance in power stability and overall compact structure indicates that diode wing-pumped Ho: YLF laser has great value in gas sensing and precise medical treatment that require a relative high stable output laser.

In this paper, factors influencing the performance of high-gain Nd:YVO4 amplifiers are analyzed and a schematic map of the relationships between different factors is given. A model, including the pump absorption saturation effect and overlap efficiency along the beam propagation direction, as well as non-radiative decays due to high doping concentration, is developed. The performance of laser amplifier is studied by changing doping concentration, pump beam quality, and focal size of pump laser. To get high gain, samples with low doping concentration should cooperate with long crystals and laser diodes with good beam quality. Based on the model, the focal radius of pump laser could be optimized for different doping concentrations and beam qualities of pump laser. Experiments were conducted and the results agreed well with the simulated ones. Moreover, a single-stage and single-pass amplifier was realized, achieving a small-signal gain of 51 dB.

In this paper, the theoretical quantitative energy-level character and the experimental laser performance of resonantly fiber-coupled diode-pumped Ho3+: YLiF4 (Ho: YLF) laser are first presented. More precise 2.7-level character of diode-pumped Ho: YLF laser can be acquired with our theoretical analysis. With the experimental study, a maximum slope efficiency of 88.5%, corresponding to an output power of 1.85 W, was obtained. In actively Q-switched operation, a maximum pulse energy of 0.3 mJ was achieved at the repetition frequency of 5 kHz with a minimum pulse duration of 160 ns. At a maximum repetition frequency of 100 kHz, a pulse energy of $16~\mu \text{J}$ was achieved with a pulse duration of 816 ns. Both the performance in continuous-wave and Q-switched regimes indicates that the current resonantly fiber-coupled diode-pumped Ho: YLF laser has great potential in certain conditions that require several watts of average output power.

An electrooptically Q-switched Nd:YLF laser end-pumped by an 880-nm laser diode with high energy and short pulsewidth at 1 kHz is demonstrated. The asymmetry of the focal lengths of thermal lens along the $a$ -axis and $c$ -axis is observed, and the cylindrical lens is used to compensate for the thermal lens effect along the $a$ -axis. We experimentally studied the performance of the Nd:YLF laser with different combinations of the output coupler transmission $T$ and the focal length $f$ of cylindrical lens. With $T=40\%$ and $f=300\ \text{mm}$ , 9.5-mJ pulse energy, 9.5-ns pulsewidth, and beam quality factors of $M_{x}^{2}=1.74$ and $M_{y}^{2}=1.97$ are obtained. Moreover, the relationships between the pulse width and pump power as well as beam transverse mode were experimentally studied and discussed.

In this paper, a wavelength-locked 878.6-nm pumped acoustic-optically Q-switched Nd:YVO4 laser is presented. A master oscillator power amplifier configuration with two-stage amplifiers is employed to scale the output power. Both the oscillator and the power amplifiers are directly pumped by a wavelength-locked 878.6-nm laser diode, reducing the thermal load of the laser crystal. The maximal output power is 120.8 W at the repetition rate of 100 kHz, with the M2 factor of 1.31 and 1.30 in two directions. The maximal pulse energy of 4.85 mJ and the shortest pulsewidth of 15 ns are achieved at the repetition rate of 20 kHz, with near diffraction limited output. The global optical-optical efficiencies are 37.7% and 47% at the repetition rate of 20 and 100 kHz, respectively. The laser has excellent output stability in a specific range of time and temperature. The output power is very stable during the five operating hours, and it is insensitive to the temperature variation of the water chiller from 15 °C to 35 °C.

We demonstrate a 1064 nm, mJ-level, sub-nanosecond end-pumped Q-switched laser with weak feedback and high gain. We obtain the pulse duration of 449.7 ps, namely 1.2 times of the round-trip time, as well as the maximum energy of 0.26 mJ at the repetition rate of 1 kHz. The pulse energy is further scaled to 3.6 mJ by a double-passed amplifier, resulting in the peak power of 8.1 MW at the highest repetition rate of 2 kHz. Moreover, both the classical Q-switching theory and weak-feedback Q-switching theory are utilized to analyze the experimental results. The simulated results support that the Q-switched lasers with weak feedback and high gain, is effective for approaching single roundtrip time, which is the pulse duration limit. Smaller pulse duration is expected by virtue of this simple and compact configuration.

The thermal lens effect of Nd:YLF crystal for different polarized beams is experimentally and theoretically studied in this paper. In the experiment, the different thermal lens effects of Nd:YLF crystal along a and c axes for π- and σ-polarized probe beams are observed, and the values of the focal lengths are measured. The theoretical analysis is made to explain the extremely weak thermal lens effect along the c axis, as well as that for the σ-polarized beam. And it is corroborated that the complementation among the thermo-optical coefficient, the thermal end bulging and the photoelastic effects contributes to the weak and asymmetry thermal lens effect of Nd:YLF crystal.

In this paper, we demonstrated a hybrid master oscillator power amplifier (MOPA) laser with high peak power and widely tunable pulse repetition frequency (PRF) and pulse duration. The first-stage solid-state amplifier was carefully designed to keep good beam quality and supply high gain simultaneously. The maximum peak power of 760 kW was achieved with average power of 42 W, PRF of 50 kHz, pulse duration of 1.1 ns, and near-diffraction limited beam quality. The MOPA laser covers a broad tunable temporal range with 1-100 ns for pulse duration and 50 kHz-1 MHz for PRF. Moreover, we experimentally and numerically figure out that Nd:YVOsub4/subcrystal behaves as if continuous-wave (CW) amplification takes place when PRF is larger than 30 kHz.

A new scheme of laser oscillators is proposed by utilizing quasi-waveguide tandem multi-crystal configuration. The optimized tandem four-crystal scheme can reach 72.1 W near TEM 00 output with the highest optical-optical efficiency of 57.0%.

We first demonstrate the laser performance of a compact 2.06 μm Ho: YLF laser resonantly pumped by a broadband fiber-coupled diode. In continuous-wave (CW) operation, maximum output power of 1.63 W, corresponding to a slope efficiency of 89.2%, was obtained with a near diffraction-limited beam quality. In actively Q-switched operation, maximum pulse energy of 1.1 mJ was achieved at the repetition frequency of 100 Hz. The minimum pulse duration was 43 ns. The performance in both the CW and Q-switched regimes indicates that the current fiber-coupled diode in-band pumped Ho: YLF laser has great potential in certain conditions that require several watts of output power or several millijoules of short pulse energy.

Intestinal ischemia-reperfusion (I/R) injury can occur in clinical settings such as organ transplantation, cardiopulmonary bypass and trauma. The noble gas helium attenuates I/R injury in a number of animal organs and thus may offer a strategy for reducing I/R-induced intestinal injury in clinical settings. In the present study, we used four different helium preconditioning (HPC) profiles to investigate the potential beneficial effect of HPC on I/R-induced intestinal injury. Male Sprague-Dawley rats were pretreated with three cycles of air breathing for 5 min combined with three cycles of breathing a 70% helium:30% oxygen mixture for either 2, 5, 10, or 15 min, after which they were subjected to 60-min intestinal ischemia and 60-min reperfusion. Sixty minutes after reperfusion, the intestinal tissues of the variously treated rats were analyzed using histology, immunohistochemistry, terminal dUTP nick-end labeling staining, myeloperoxidase activity assay, Western blotting, and enzyme-linked immunosorbent assay for tumor necrosis factor α and macrophage inflammatory protein 1α. Intestinal permeability was assayed by measuring fluorescein isothiocyanate-dextran release in blood samples. The results showed that the HPC profile consisting of three cycles of 10 or 15 min of helium breathing and three cycles of 5 min of air breathing reduced I/R-induced intestinal injury, cell apoptosis, and the inflammatory response. However, the 2- or 5-min helium breathing did not confer any protective effects. It seems that longer helium episodes should be used in HPC profiles designed to attenuate intestinal I/R injury.

We first demonstrate the laser performance of a Cr2+:CdSe passively Q-switched (PQS) 2.09 μm Ho: YAG laser resonantly pumped by a thulium-doped fiber laser. The maximum output pulse energy of 1.766 mJ, corresponding to a repetition frequency of 685 Hz, was obtained with a pulse duration of 15.4 ns. The pulse peak power was 114.7 kW, while the PQS efficiency was 21.45% against the continuous-wave output. The laser wavelength in the PQS operation was precisely measured to be 2090.2 nm.

We demonstrated the active shaping for a solid-state Nd:YVO4 amplifier with a high average gain of 39.2 dB. The average output power was 8.3 W with respect to the input power of 1 mW. A range of common and useful pulse shapes was generated at the final output. In addition, a very flat square pulse was produced with a root-mean-square less than 3% in amplitude. A numerical method was proposed to realize active shaping without an experimental test for the Nd:YVO4 amplifier, showing great potential for the design of lasers with both high peak power (>100 kW) and a desired pulse shape.

In this paper, the performance of an end-pumped laser amplifier was experimentally studied by adjusting the pumping wavelength of a laser diode. An interesting phenomenon was observed: that the gain would decrease with an increase in absorbed pump power. The scaled output power of 0.3 at. % doped 20 mm long Nd:YVOsub4/subcrystal decreased from 0.48 to 0.2 W when the absorbed pump power increased from 17.5 to 17.8 W. Theoretical analysis was demonstrated according to our previous model. The long crystal length is the main reason for the observed phenomenon. This phenomenon could be utilized to enhance amplifier gain and improve thermal performance, including the maximal temperature and thermal stress of the crystal.

In this paper, we compare pulse parameters in two end-pumped passively Q-switched lasers by increasing the boundary temperature of the laser crystal. For the Nd:YAG/Cr:YAG laser, the pulse energy at 1 kHz increased from 12.4 to 21 μJ when the boundary temperature increased from 20°C to 120°C, while the pulse width decreased by 1.2 times. For the Nd:YVO4 passively Q-switched laser using Cr:YAG as the saturable absorber, the pulse energy at 100 Hz increased from 5.45 to 24.5 μJ when the boundary temperature increased from 26°C to 113°C, while the pulse width decreased by 2.4 times. An improved model based on the rate equations was introduced to analyze the large variation of pulse energy when heating the Nd:YVO4 crystal.

The 30 at.% Ho: BaY2F8 crystals were grown by the Czochralski method, and their spectroscopic properties are analyzed systematically by standard Judd–Ofelt theory. The Judd–Ofelt intensity parameters are estimated to be Ω2 = 6.74 × 10−20 cm2, Ω4 = 1.20 × 10−20 cm2, and Ω6 = 0.66 × 10−20 cm2, and the fluorescence branching ratios and radiative lifetimes for a series of excited state manifolds are also determined. The emission cross sections with our measured infrared luminescence spectra, especially important for 4.1 μm, are calculated to be about 4.37 × 10−21 cm2. The crystal quality is preliminarily tested through a mid-infrared laser emission experiment.

A semi-analytical calculation framework is proposed to calculate the eigenmodes of a general laser resonator with arbitrary intra-cavity wavefront aberrations. By solving a linear eigenvalue equation in the complex space, the mode intensity distributions of the eigenmodes in high power unstable resonators are obtained, indicating that due to the aberrations the area of fundamental mode significantly shrinks to form the localized mode with extremely high power intensity. The beam quality, mode area, threshold gain, and operation reliability are compared between the traditional unstable resonator and the one with a graded reflectivity mirror. The simulation results disclose that with a graded reflectivity mirror more high-order modes participate in mode competition and the localized mode effect of fundamental mode is weakened.